1. Field of the Invention
The present invention relates generally to a vibration damping device filled with non-Newtonian fluid which exhibits rheopectic properties. More particularly, the invention relates to an improved arrangement which permits the damping characteristics to be controlled by sensing acceleration in the vertical direction of a vibrating body which acceleration varies with the vibration of the vibrating body and which produces a suitable control signal applied to the damping member.
2. Description of the Prior Art
Recently, there have been proposed and developed various vibration damping devices which are filled with rheopectic fluid and which are capable of varying viscosity of the fluid within a passage defining fluid chambers with the result that the resonance frequency of the damping member may be selectively varied. One such vibration damping device has been disclosed in the Japanese Patent First Publication (Tokkai Showa) 60-104828. This conventional damping device is comprised of a rigid annular member on which an elastomeric member and a flexible diaphragm are supported in such a manner as to define an enclosed space which is filled with the rheopectic fluid. A partition member is interposed in the internal space to define first and second chambers. The partition member includes electrodes which are juxtaposed to each other in a fluid passage defined within the partition member. These electrodes are connected to a control circuit which selectively applies a voltage thereacross.
FIG. 1 is a model illustrating a system of vibrating members having a single degree of freedom, comprised of a spring K and a damper C. The spring K and damper C are juxtaposed between a vibrating body (engine) m and a base. In this model, reference numeral Fk denotes the spring force along the axis of vibration of the vibrating body and reference numeral Fc denotes the damping force of the damper C. F.sub.total denotes the vibrational force which is transmitted through the damping device to the base and which is equal to Fk+Fc.
FIG. 2 is a graph showing the relationship between the spring force Fk, the damping force Fc, and the transmitted vibrational force F.sub.total as shown in FIG. 1.
t.sub.o is the initial time of the measurement of the spring force Fk and T is the length of one vibration cycle measured from the initial time t.sub.o.
As clearly shown in FIG. 2, the phase difference between the spring force Fk and the damping force Fc, is 90.degree. or T/4. This is because the spring force Fk is proportional to the displacement of the sprung mass and the damping force Fc is proportional to the velocity of the sprung mass. In such a system, it is easy to calculate the damping force at any given moment.
In damping devices wherein a fluid is arranged to flow through a fluid passage between the first and second chambers, the flow of fluid induces expansion of an elastomeric and a flexible diaphragm in such a manner that the resilience of the members defining the first and second chambers has the effect of an expansion spring. The phase relationship between the spring force and the expansion spring force in such devices is complex and difficult to calculate. If the flow resistance of the passage between the respective chambers is changed, the resonance frequency of the expansion spring changes, still further complicating the phase relationship between the spring force and the expansion spring force, making it difficult to calculate the fluid passage resistance that will produce the optimum damping effect.